Cam followers like other parts of the internal combustion engine have been the subject of extensive variation and development. In addition to variations in useful configurations, cam followers have been made by numerous processes, including casting, stamping, forging and combinations of the same, including the use of machined parts such as needle bearings or the like.
Generally, cam followers are supported for pivotal movement in order to directly or indirectly receive the reciprocating drive provided by a camshaft which urges the cam follower against a spring biased member, resulting in the opening and closing of an intake or exhaust valve. Problems to be solved in engineering such cam followers include avoiding undue wear, reducing friction, and providing for ease of replacement.
An example of such a cam follower can be found in U.S. Pat. No. 4,697,473 to Patel which will be discussed in more detail in connection with the attached drawings. The Patel structure employs an elongated cam follower of inverted-U cross-section which supports a cam-engaging cam follower roller in bearings. The bearings transmit the valve-driving load, which has to be sufficient to compress the valve springs. Efficient lubrication of these bearings, and of any cam-engaging surfaces, is therefore critical to engine life. Such lubrication problems are exacerbated by modern standards of automobile durability which commonly expect passenger automobile engines to run 100,000 miles or more without failure or major service.
When the Patel cam follower is disposed at a substantial incline, it allows oil to flow over its back from a lifter post supporting one end of the cam follower towards the generally vicinity of the cam follower bearings. This requirement for an inclined cam follower has the drawback of restricting the applicability of the Patel structure to inclined engines in which one or more cylinder banks is substantially out of the vertical, as is the case in a V-aligned engine such as a V-6 or V-8 engine and of rendering it unsuitable for use in engines having one or more upright banks of cylinders. Such lubrication may also fail temporarily on extended banked curves or when climbing up hill (a situation where engine stress is maximized), depending upon the particular engine disposition, longitudinal or transverse.
As a safeguard lubrication through the cam is generally desirable with the Patel construction, a relatively expensive complication bringing further drawbacks.